1. Field of the Invention
The present invention relates to a wiring board, a semiconductor device, and a process for the production of wiring boards, and particularly to an effective technology applied to a semiconductor device of LGA (Land Grid Array) type.
2. Prior Art
Heretofore, there has been semiconductor device of CSP (Chip Scale Package) type wherein a ball-like bump (ball terminal) is connected as an external connection terminal for connecting the semiconductor device to a mount board such as a mother board, or an external device as the one wherein a semiconductor chip has been mounted on a wiring board.
The above-described semiconductor device of CSP type is arranged as shown in, for example, FIGS. 1A and 1B, in such that a wiring board in which an electric wiring 2 and an external connection terminal 2A are disposed on a first principle plane (a side of the front) of an insulating substrate 1 such as a polyimide tape is placed, and a semiconductor chip 6 is mounted on the surface on which the electric wiring 2 of the wiring board (the insulating substrate 1) has been formed in, for example, such a manner that its external electrode 601 is opposed to the above-described surface wherein the electric wiring 2 of the above-described wiring board is connected with the external electrode 601 through a protrusion conductor 13. FIG. 1B is a sectional view taken along the line C-C′ of FIG. 1A. Further, a gap between the wiring board (insulating substrate 1) and the semiconductor chip 6 is subjected to under-filling sealing by means of a sealing insulator 9 made of, for example, an epoxy-based thermosetting resin and the like in the above-described semiconductor device. Besides, an opening 101 for connecting a ball terminal is defined at a predetermined position of the insulating substrate 1, for example, a site where, for example, the external connecting terminal 2 has been disposed, and it is guided to a second principal plane opposed to the first principal plane by means of a through hole plating 15 provided around the opening 101 or a conductive member filled inside the opening 101. To the opening 101, a ball terminal 16 made of, for example, a Pb—Sn based solder and the like is connected.
In case of the above-described semiconductor device of CSP type, however, when the ball terminal 16 of the semiconductor device of CSP type is connected with an electric wiring 11 of a mount board 10 such as a mother board to mount the semiconductor as shown in FIG. 2, a height t extending from a mounting surface 10A of the above-described mount board 10 to the upper surface 6A of the semiconductor chip 6 in the semiconductor device becomes higher by an amount corresponding to a height t′ of the above-described ball terminal 16. For this reason, a container (casing) for containing the amount board 10 on which the above-described semiconductor device of CSP type has been mounted becomes thicker, so that it is difficult to reduce a size of the semiconductor device.
Moreover, since the external electrode 601 of the above-described semiconductor chip 6 is connected with the electric wiring 2 by means of the protrusion conductor 13 in the case when the semiconductor chip 6 is subjected to flip-chip junction on the wiring board, a distance (stand-off) extending from the insulating substrate 1 to a circuit-forming surface of the semiconductor chip 6 becomes higher, so that the semiconductor device becomes thicker, whereby it is difficult to thicken the same.
In this connection, there is a semiconductor to LGA type wherein an unrelieved external connecting terminal is disposed in place of the above-described ball terminal 16 as a manner for preventing from an appearance of a thicker semiconductor device. In the above-described ball terminal 16 as a manner for preventing from an appearance of a thicker semiconductor device. In the above-described semiconductor device of LGA type, an electric wiring 2 is formed on a principal plane of an insulating substrate 1, and an external connecting terminal (land) 17 is formed on a surface opposed to the surface on which the electric wiring of the above-described insulating substrate 1 has been formed as shown in FIG. 3. In this case, the electric wiring 2 is electrically connected with the land 17 by means of a through-hole plating 15 provided around a via hole 102 defined on the above-described insulating substrate 1. The outer periphery of the land 17 may be covered with a protective film such as a solder resist. In case of the above-described semiconductor device of LGA type, a plating layer 4B prepared by laminating a nickel plating layer and a gold plating layer having good solderability on a surface of the land 17. In this respect, a soldering paste or the like has been previously applied onto a predetermined position of the surface of the above-described land 17 or the electric wiring 11 on a mount board 10, and then, the semiconductor device is mounted.
In case of such a semiconductor device of LGA type, since there is no ball terminal 16 as in a semiconductor device of CSP type, a height of the semiconductor device can be reduced in the case when it is mounted on the mount board 10, whereby the present semiconductor device can be made thinner than that of the above-described semiconductor device of CSP type.
A wiring board used in the above-described semiconductor device of LGA type is prepared as described hereinafter. First, conductive thin films 18 made of a copper foil and the like are formed both principal planes of an insulating substrate made of a polyimide tape and the like, the conductive thin film on a side of either principal plane is etched to form an external connection terminal 17, and then, a via hole 102 is defined at a predetermined position of the above-described external connection terminal 17 by means of laser or the like as shown in FIG. 4A.
Thereafter, a through-hole plating 15 is formed around the via hole 102 as shown in FIG. 4B, and an electric wiring 2 is formed from the conductive thin film 18 on the surface opposed to that on which the above-described external connection terminal 17 has been formed by the use of, for example, an additive plating method or the like method. In this occasion, a connection terminal 2A, which is to be connected to a through-hole plating 15 in the above described via hole 102, is formed on the electric wiring 2.
Then, as shown in FIG. 4C, a plating layer 4A prepared by laminating, for example, a nickel plating layer and a gold plating layer is formed on a surface of the above-described electric wiring 2 as well as a plating layer 4B prepared by laminating, for example, a nickel plating layer and a gold plating layer is formed on a surface of the above-described external connection terminal 17. A wiring board used for a semiconductor device of LGA type is obtained in accordance with the procedure as described above.
For instance, a semiconductor chip 6 is subjected to flip-chip mounting on a surface on which the electric wiring 2 of a wiring board prepared in accordance with the above-described procedure has been formed, and a liquid resin is poured in between the above-described wiring board (insulating substrate 1) and the semiconductor chip 6 to complete under-filling sealing, whereby a semiconductor device of LGA type can be obtained as shown in FIG. 3.
In a semiconductor device of CSP type shown in FIG. 1, however, it is required to maintain certain spacing in between the openings 101 so as not to be in contact with the ball terminals 16 each other. The same situation is observed in also the semiconductor device of LGA type shown in FIG. 3 wherein it is required to maintain a certain spacing in between the via holes 102 so as not to be in contact with the external connection terminals (lands) 17 each other. In this respect, via holes 102 must be formed with a certain spacing from a constructional point of view in case of any of the semiconductor devices above, otherwise it results in a drawback for downsizing of its package.
Furthermore, in a conventional semiconductor device of LGA type described above, the electric wiring 2 is formed on a principal plane of the insulating substrate 1, and the external connection terminal (land) 17 is formed on the surface opposed to that on which the electric wiring has been formed in case of preparing a wiring board for mounting a semiconductor chip. In this constitution, a tape material wherein a conductive thin film such as a copper foil has been disposed on the opposite surface of the insulating substrate 1 is employed. For this reason, there has been such a problem that its material cost increases, besides its manufacturing steps increase, so that the resulting manufactures' costs for wiring board and semiconductor device increase.